Signaling system



VOLTAGE A ril 15, 1941. w. H. T. HOLDEN 2,238,469

SIGNALING SYSTEM Filed Aug. 9, 1939 2 Sheets-Sheet 1 FIG! cannot mvoasVOL nae 2 ap nox. 170

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TO CONNEC TOR T0 FIFST SELECTOR T0 NEXT FINDER INVENTOR W/'/. 7. HOLDENATTORNEY V Patented Apr. 15, 194-1 SIGNALING SYSTEM William H. 'r.Holden, Long Island City, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication August 9, 1939, Serial No. 289,147

8 Claims.

This invention relates to signaling systems and particularly tosignaling in telephone systems.

This application is a continuation in part application of my applicationSerial No. 246,794, filed December 20, 1938.

An object of the invention is to improve the signaling over telephonelines in response to closing of a connection between the line conductorsat a substation.

Another object is to eliminate as far as possible the disturbing lineconditions that may be present while signaling over a telephone line.

Another object is to improve central oflice equipments in automatictelephone systems by substituting a simplified and more efficient signalresponsive circuit arrangement in place of the usual line relay, and bysimplifying the testing equipment for line finders.

Heretofore systems have been employed in which the closing of aconnection between the line conductors at a substation causes theoperation of a line relay or similar apparatus at the central ofice toinitiate telephone connections. In such systems any line attenuationssuch as station ground, potentials, or other leakages may disturb orinterfere with the proper functioning of the line relay, that is, therelay may respond or release at irregular intervals due to currentchanges caused by such disturbances on the line.

This invention relates to arrangements for eliminating disturbanceswhile signaling, over telephone lines and it is a feature of the presentinvention to substitute in place of the usual line relay, a circuitarrangement at one end of the line whereby a start relay or othersignaling devices may be operated in response to a change in reactanceof the line when a connection is closed between the line conductors atthe opposite end of the line.

Another feature of the invention is an arrangement whereby signaling iseffected by a phase shift of the ionizing voltage on a control electrodeof a cold cathode tube in response to a change in reactance of atelephone line when a connection is established between the lineconductors thereof. I

Another feature is a method of signaling over a telephone line inresponse to a discharge of a cold cathode tube comprising subjecting ofthe tube to an ionizing voltage condition that is normally out of phasewith respect to the discharge voltage of the anode t normally preventthe discharge of the tube to take place and shifting the phase of saidionizing voltage to cause a discharge to take place through the tubewhen minals 5 of a connector 6.

the effective discharge voltage is present on the anode. The arrangementmay be such that this phase shift is accomplished by the change inreactance resulting fromclosure of the line at I a subscribers station.

Another feature of this invention relates to a line-finder circuitarrangement including means for testing for the calling line over thetalking circuit to cause the line finder to stop on the terminals of thecalling line. It includes a cold cathode tube associated with one of thetalking conductors which is caused to discharge when the calling line isfound by the line finder and circuit means controlled by said tube tostop the'line'finder. I

This invention has been illustrated in the accompanying drawings inwhich:

Figs. 1 and 3 show an automatic telephone system in schematic form withthe applicants invention applied thereto. Fig. 1 shows a line circuit inwhich a circuit equipment according to the applicants invention issubstituted for the usual line relay to operate a start relay and Fig. 3shows a line finder including a testing equipment in accordance with theapplicants invention.

Fig. 2 is a sine wave diagram indicating voltage and phase shiftconditions to illustrate the functions in this respect of the applicantsinvention.

Referring now to the drawings, Figs. 1 and 3 show a telephone set I anda line 2 leading to a central office where the line is connected to theterminals 3 of a line finder 4 and to the ter- The usual cut-ofi relay Iis connected to the sleeve terminal of the line finder and connector andthe line extends through contacts of this relay to the equipmentprovided for the substitution of a line relay comprising a repeatingcoil 8, alternating current sources 9 and I0, cold-cathode dischargetube ll, resistances I2 and I3 and a common start relay l5. This relaymay be operated when the subscriber at station I removes his receiverfrom the 'switchhook to close the usual start circuit for causing theline finder 4 to function to eX- tend a connection from the subscribersline I to the usual automatic equipment for establishing a connection toa called line by the operation of the dial at substation I. When callscome in over the connector 6, the cut-off relay 1 is operated to removethis equipment from the line and a connection may be established to acub scribers line I ihth liSllfil manner. 7

This equipment for operating the start relay I when a subscriber removeshis receiver from the switchhool: is so arranged that the discharge tubeII is connected in a circuit that normally prevents the tube frombreaking down, but permits a breakdown to take place to close anoperating circuit for the relay I5 when the line circuit is closed. Thiscircuit arrangement utilizes a resistance-impedance series combinationin which normally a resistance factor only is employed to prevent thetube from discharging and both resistance and impedance factors areemployed to permit the tube to discharge. The resistance factor is aresistance element normally in the circuit and the impedance factor isfurnished or represented by the line when closed at a substation. Withthis arrangement a system is provided that permits the relay I5 tooperate more or less independently of earth potentials or station groundconnections, or leakances, or other characteristics of the line.

To this end the tube II has one element, that is, the cathode I6,connected through the winding of the relay I5 to ground and anotherelement, that is the main anode I'I, connected to one terminal of thealternating current source ID, the other end of which is connected toground. The third element, that is the control electrode I8, isconnected to resistance I3. This resistance I3 is coupled to aresistance-impedance circuit comprising two branches. two conductors ofline 2 through the subscriber's loop over the contacts of relay 1 andone winding is of the repeating coil 8 to the positive side of thedirect current battery 20, the negative side of which is connected toground. The other branch includes the high resistance I2 and anotherwinding 2| of the repeating coil 8 to the positive side of the directcurrent battery 20. Another winding 22 of the repeating coil 8 isconnected in series with the alternating current source 9.

In general, the operation of this device is as follows: normally withthe line opened the alternating current source I0 establishes anelfective voltage drop on the main anode I1 and the alterhating currentsource 9 establishes an effective voltage drop on-the control electrodeI8. These effective potentialson the main anode I1 and control electrodeI8 are normally out of phase. That is to say, the effective voltage onthe control electrode I8 to ionize the tube I I will not occur at thesame time as the efiective voltage on the main anode I'I occurs whichwould therefore prevent the tube from operating under normal conditions.On the other hand, when the line conductors 2 are closed at thesubstation, the resistanceimpedance circuit provided thereby willoperate to change the phase of the effective voltage on the controlelectrode I8, so that it occurs at the same time as the effectivevoltage on the main anode I'I. Consequently, the tube will operate underthese conditions to cause a current to flow through the tube from themain anode I! to the cathode I6 through the winding of relay I5. Whilethe phase relation between the voltages on the control electrode I8 andthe main anode I1 is nor mally fixed bythe resistance-impedance circuitwhen the line is opened, this phase relation may vary considerably dueto line conditions when the line is closed and yet cause the tube tooperate. Although it is, of course, necessary in order to cause the tubeto operate to move the phase of the voltage on the control electrode I8sufiiciently close to that on the main anode H to cause the ionizationof the tube to take place within the interval when the voltage on theOne branch includes the main anode I7 is effective to cause the tube tobreak down.

More specifically, this deviceoperates as follows: The operating currentsources 9 and ID are so controlled that the waves produced by thesesources normally bear a definite phase relation. However, due to theresistance I2 and the reactance of the line 2 in the circuits for thecontrol electrode I8, the phase of the voltage applied on this electrodeis caused to lag behind the phase of the voltage applied on the mainanode I'I. The control electrode voltage drop is that effected betweenthe points 23 and 24. Furthermore, this voltage on the control electrodeI8 is normally sufficiently biased by the connection at point 23 of thepositive terminal of the direct current source 20. Thus the tube II isprevented from operating due to the fact that the voltage supplied bythe alternating current source II) on the main anode I! cannot cause adischarge to take place between this anode and the cathode I6 during itseffective period as the control electrode voltage will not besufiiciently' positive in respect to the cathode I6 to cause ionizationof the tube during this effective period. In other words the main anodevoltage is not sufficiently positive to cause the discharge of the tubeduring the ionization period.

This is the characteristic under normal condition when the line is open.On the other hand, when the connection is made at the substation betweenthe conductors of line 2 it will be observed that it is made over acircuit across the points 23 and 24. This closure of the direct currentloop at the substation produces, in effect, a substantial change in thereactive impedance of the line. This change causes the control electrodevoltage to shift in phase to be nearly or fully in phase with theeffective voltage of the main anode I'I. Consequently, the ionization ofthe tube by the positive characteristics of the control electrode willtake place at the time when the positive voltage on the main anode I1 issufficient to cause a discharge between the anode I1 and cathode IS. Thetube will therefore discharge at this time as long as the voltage on theanode I1 is sufiicient to maintain it. A current will consequently nowflow from the source I0 between anode I1 and cathode I6 over the circuitthrough the winding of relay I5 to ground and cause this relay tooperate. This current will therefore comprise a series of direct currentbeats continued as long as the line circuit is closed to maintain thetube operated, and relay I5 is designed to operate and hold on thesecurrent beats.

This phase shifting function has been illustrated in the sine wavediagram of Fig. 2. The wave form 30 illustrates the voltage on the mainanode I I. The normal voltage on the control electrode I8 is illustratedby wave form 3I which, being biased by battery 20, has its zero line at32. This shows that when wave 3| is thus out of phase or lags behindwave 30 for about degrees the tube will not become conducting as theionization across the control electrode I8 and cathode I6 ceases beforethe effective voltage on the main anode I! has risen sufficiently tostrike or discharge to the cathode I6. However, when the controlelectrode voltage is shifted to take the position indicated by wave 33approximately 25 degrees towards the right the voltage on anode I! hasrisen to a value where it will strike, that is, the tube willdischarga'and as indicated by wave 34, the com --brushes are oppositethe-terminals 3 of the trol anode voltage may shift about 135 degreesfurther towards the right before the tube ceases to strike. Hence, theremay be considerable change in the line attenuations without causing anyfalse operations of the start relay.

Although any suitable means may be used for signaling the subscriber atthe substation, an alternating current ringer is illustrated. This bellmay be designed to respond readily to the ringing current frequency andto be unrespone sive ,to current of the frequency produced by generator9. r

A description will now be made of the function of the line-findercircuits as disclosed in Fig.

3 whereby a connection may be established from the calling line in Fig.1, when the line circuit has functioned to operate start relay l5 ashereinbefore described, to cause this line finder to operate to seizethe calling line and connect it through line terminals 3 and line-finderbrushes 49 to a connection beyond. This line finder is of the well-knowntype which operates in a vertical direction to advance its brushes 49 tothe level in the switch in which the calling line is located and tothenadvance the brushes in a rotary direction to connect them with theterminals of the calling line. The testing for the calling line will becontrolled primarily by the coldcathode tube 4| and associated circuitsover the ring terminal and ring brush as will hereinafter be described.When relay l5 operates the effect will be that a start circuit is closedfor the operation of relay 42 over a circuit from battery, winding ofthis relay, the usual eleventh step contacts 43, contacts of relay 44 toground at the contacts of relay l5. When relay 42 operates it opens apoint in the circuit of release magnet 45 and places ground potential onthe conductor 48. This prepares a locking circuit for relays 47 and 44and operates the vertical magnet 48 over a circuit from battery,contacts of interrupter relay 49, winding of magnet 48, the lower outercontacts of the transfer relay 41 to ground at contacts of relay 42 overconductor 46. relay 49 at its contacts, whereupon relay 49 operates andopens the circuit from magnet 48. Magnet 48 thereupon deenergizesandopens the circuit for relay 49 whereupon relay 49 deenergizes and againcloses the circuit for magnet 48. 4'

These actions continue untilthe circuit for this magnet is opened on theoperation of relay 4! which takes place when the magnet has advanced thevertical wiper 50 to the third level of bank contacts 5|. 59 is broughtinto engagement with the test contact 52. When this occurs a circuit iscompleted for relays 41 from battery through its winding, wiper 50,contact 52, contacts of relay IE to ground. Relay 41 in operating closesa locking circuit for itself through its inner lower armature and frontcontact to ground over conductor 46 at contacts of relay 42. Relay 4!also opens the circuit for the vertical magnet 48 and thereby terminatesthe vertical movement. Relay 41 now extends the ground connection fromrelay 42 over conductor 46 to the rotary magnet 53 which operates over acircuit from battery, contacts of relay 49, winding of magnet 53 andcontacts of relays 44, 41 and 42 to ground over conductor 46. The rotarymagnet in operating closes a circuit for the operation of relay 49 whichopens the rotary magnet circuit so that this magnet releases and causesthe release of Magnet 48 in operating closes a circuit for 73.1

In this position the Wiper relay 49. These actions are continued untilthe 75 calling line;

It should now be observed that the control electrode 55 of thecold-cathode tube 4| is connected to the ring brush of the line finderthrough a resistance 56 and over the ring terminal of the calling line,ring conductor, contact of relay 1 to the point 24. As has already beenexplained, when this line is calling the phase relation between thealternating current voltages as applied by the source 9 to ID cause tubeH to operate. Consequently, as resistance 56 is of the same value asresistance l3 and both being connected to the same point 24 in thecircuits and as the phase of the alternating current source 5| connectedto the main anode 58 of tube 4| is the same as that of the alternatingcurrent source ||l, it follows that the voltage on control electrode 55will now cause tube 58 to operate for the same reason as tube operateswhen the subscriber calls. It should be noted that the operation of tube4| will only take place when a called line is encountered. In case thebrushes encounter idle lines during their travel to the terminals of thecalled line, it is evident that the phase of the alternating currentvoltage as applied at points corresponding to point 24 of such lines andthe anode voltage of tubes such as H are out of phase and such tubes arenot operated as hereinbefore explained. Consequently, under thesecircumstances tube 4| can not operate. It is also evident that when thebrushes 40 encounter busy lines, the tube 4| will not operate as therelays corresponding to relay 1 of such busy line would be operated andthus the tubes corresponding to tube I would be eliminated from thecircuit. Resistances l3 and 55 are so high that the control electrodecurrent of tube I. does not appreciably alter the phase angle nor doesthe connection of the control electrode of tube 4| through the ringconductor of a busy line produce any appreciable disturbance. When tube4| operates the resulting current through the tube over main anode 58and the cathode 59 flows through the upper winding of relay 44 frombattery through the upper winding of relay 44, cathode 59, main anode 58and source 51 to ground. This current will, of course, comprise a seriesof direct current beats continued as long as the tube 4| is in operativecondition. Relay 44 in operating provides a locking circuit for itselfthrough its lower winding, lower inner armature and front contact,contacts of relay 42 over conductor 45, and opens the circuit for therotary magnet 53 so that the line finder will therefore remain connectedto the calling line terminals. Relay 44 now extends the connection fromthe calling line, over terminals 3 and brushes 40 through contacts ofthis relay to a first selector for the establishing of a connectionbeyond as is well known in the art. Relay 44 also extends the startingwire from relay l5 to the next finder. When ground is encountered overthe sleeve conductor from the first selector, relay 60 operates frombattery over the upper winding and provides a connection to ground formaintaining th relay 42 operated. After the starting ground is removedby the operation of relay 44, relay 42 is slow in releasing so as toremain operated during the transfer of the connection. This groundconnection of the sleeve from the first selector also causes theoperation of relay 1 Which disconnects, as hereinbefore described, theconnection from the calling subscriber" to tube l which new ceases tooperate and releases relay 15 to open the starter wire and theconnection to contact 52. Consequently, tube 4| also ceases to operateand current through the upper winding of relay 44 is discontinued.

The connection established from the calling subscriber over the linefinder to the first selector may now be extended through a calledsubscriber in the usual manner through any well-known automatictelephone system by having the subscriber dial the called subscribersnumber. When the connection is released, ground is removed from thesleeve connection and thus causes the release of relays 60 and 42 whichin turn causes the release of relays 4'! and 44. Ihe release of relay 42closes a circuit for release magnet 45 from battery through the windingof this magnet and vertical off-nornial contacts 6|, contacts of relay42 to ground. Release magnet 45 restores the line finder to normal. Itis evident that this relay 60 will not cause the release of the linefinder if the starter wire is used for operating another succeeding linefinder at the time the circuit for the upper winding of relay 60 isopened as it will be locked from battery through its lower windingthrough the starter wire ground. This locking circuit will, of course,be open when the starter wire is no longer needed at which time theground will be disconnected from this wire by the release of relay 15which takes place when the line finder has found a calling line and theassociated cut-off relay 1 is operated.

What is claimed is:

1. In a signaling system, a line comprising a pair of conductors, asignaling device, a threeeIement cold-cathode tube, means for normallythe tube will discharge during said period, and

means for actuating said signaling device when a discharge takes placebetween said anode and cathode.

2. In a telephone system, a signaling device, a cold-cathodetub'e'having a control anode, a main anode and a cathode, means fornormally applying voltage on the control anode at intervals for ionizingsaid tube at said intervals, means for normally applying a dischargevoltage on the main anode at the intervals when the tube is not ionizedthus normally preventing the tube from discharging, means for shiftingthe intervals of applications of the ionizing voltage so that they occurduring the intervals when a discharge voltage is applied to cause thetube to discharge during said intervals and means responsive to saiddischarge through said tube for actuating said signaling device.

3. In a telephone system, a relay, two line conductors, a cold-cathodetube having a control anode, a main anode and a cathode, a circuitconnecting the cathode through the winding of said'relay to ground,means for applyingvoltage to said control anode at intervals forionizing said tube during said intervals across said control anode andsaid cathode, means for applying discharge'voltage to the main anode atintervals when the tube is not ionized so that the tube will notdischarge, means including the said line conductor in series forshifting .the application of the ionizing voltage to occur during theapplication of the discharge voltage so that the tube will dischargeacross the main anode and cathode when the discharge voltage is appliedand operate the relay in the cathode circuit.

4. In a signaling system, a relay, a central oflice, a substation, atelephone line connecting said central ofiice and said substation, acoldcathode tube having a control anode, a main anode and a cathode,means including a source of alternating current, a transformer and asource of direct current associated with said telephone line andthecontrol anode of said tube for establishing an ionizing potentialbetween said control anode and said cathode at intervals, meansincluding a source of alternating current and the main anode of saidtube for establishing a voltage on said anode at intervals that causessaid tube to discharge between said main anode and said cathode when thetube has been ionized, said two means being so arranged that theintervals of ionization and the intervals of application of thedischarge voltage occur normally when the line conductors are opened atthe substation and at alternate periods to prevent discharge of thetube, and occur at the same period when the line conductors are closedat the substation to cause discharges of the tube, and a circuit fromthe cathode through the winding of said relay to ground for energizingsaid relay each time the tube discharges.

5. In a telephone system, a line, a repeating coil, a relay, acold-cathode tube having a control anode, a main anode and a cathode,circuit means comprising one section including a source of directcurrent, a secondary winding of said repeating coil and a resistanceconnected in series with the control anode and the winding of said relayconnected at one end to the cathode and at the other end to ground,another section including one conductor of said line connected to thecontrol anode, a third section including the other conductor of saidline and another secondary winding of said repeating coil, in seriesconnected to said first-mentioned secondary winding and said source ofdirect current, a fourth section including an alternating current sourceand a primary winding of said repeating coil in series, a fifth sectionincluding a source of alternating current having one terminal connectedto ground and the opposite terminal connected to the main anode, saidcircuit means being so adjusted that when the two conductors are notconnected together the tube will ionize across th control anode andcathode and a discharge voltage will be applied to the main anode atalternate intervals and thus prevent the tube from discharging and whenthe line conductors of said line are connected together, at their freeends, the ionization will occur during the application of the dischargevoltage and thus cause the tube to discharge across the main anode andcathode and cause current to flow through the relay winding to operatethe relay.

6. In a telephone system, a set of line terminals, a line finder havingbrushes controllable to connect with said line terminals, a lineconnected to said line terminals, a relay, a coldcathode tube, a circuitmeans associated with said line and tube so arranged that when said lineis seized voltage is applied to aid tube at brushes to engage with saidline terminals, a

cold-cathode tube in said line finder, means for applying a dischargevoltage on the anode of said last-mentioned tube at the same intervalthat the ionizing voltage is applied to the firstm'entioned tube, acircuit means operative when said brushes encounter said line terminalsand so arranged that the ionizing voltage applied to saidfirst-mentioned tube at intervals is applied over one of said lineterminals and a corresponding brush to said second-mentioned tube atsaid certain intervals which coincide with the intervals when dischargevoltage is applied to said second-mentioned tube and therefore causesaid second-mentioned tube to discharge, and means responsive to saidlast-mentioned discharge for causing said line finder to stop itsbrushes on said line terminals.

7. In a telephone system, a set of terminals, a line finder havingbrushes connectable to said terminals, a line connected to saidterminals, a

relay, a three-element cold-cathode tube, means for applying a voltageon the control anode of said tube for ionizing it at intervals, meansfor normally applying a voltage to the main anode of said tube atintervals intermediate the ionizing period of said tube so that the tubewill not normally discharge, means responsive to the seizure of saidline for changing the ionizing intervals of said tube to coincide withintervals of application of the discharge voltage so that the tube willdischarge during the interval when a discharge voltage is applied, meansresponsive to said discharge of the tube for operating said relay, meansin said line finder operative in response to the operation of said relayfor actuating the line finder to engage said terminals, a three-elementcold-cathode tube in said line finder, a circuit means operative when abrush of said line finder engages the corresponding terminal of saidline for causing the ionizing voltage applied to the first-mentionedtube to be app-lied to the control anode of the secondmentioned tube tocause it to ionize, means for causing said second tube to discharge whenionized, a relay, means responsive to the discharge of saidsecond-mentioned tube for actuating said last-mentioned relay, and meansresponsive to the operation of said relay for actuating said line'finderto retain its brushes on said terminals.

8. In a telephone system, a set of terminals, a line finder havingbrushes connectable to said terminals, a line connected to saidterminals, a three-element cold cathode tube associated with said line,means associated with said line and tube so arranged that when said lineis calling, voltage is applied to said tube at intervals to cause it toionize and discharge, means for also applying said ionizing voltage toone of the terminals of said line, means responsive to the discharge ofsaid tube for operating said line finder to cause its brushes to engagesaid line terminals, a three-element cold cathode tube associated withsaid line finder, means for applying a discharge voltage on the anode ofsaid lastmentioned tube at the same interval as the ionizing voltage isapplied to one of said terminals of the line, a circuit means soarranged that the ionizing voltage applied to one of the terminals ofthe line will be applied to ionize said second tube and cause it todischarge when one of said brushes of the line finder encounters saidone terminal, and means responsive to said lastmentioned discharge forstopping said line finder with its brushes on said line terminals.

WILLIAM H. T. HOLDEN.

